The invention relates to the recording of soundtracks onto analogue cinema film, in particular the recording of digital created and/or digital/electronically stored representations of soundtracks onto film.
Optical recording is the most common method employed for analogue motion picture sound tracks. This method uses a variable area method where illumination from a calibrated light source is passed through a shutter modulated by the audio signal. The shutter opens in proportion to the intensity or level of the audio signal and results in the illumination beam from the light source being modulated in width. This varying width illumination is directed to expose a monochromatic photographic film which when processed, for example, results in a black audio waveform envelope surrounded at the waveform extremities by a substantially clear or coloured film base material. In this way the instantaneous audio signal amplitude is represented by the width of the exposed and developed film track. FIG. 1 depicts in greatly simplified form an arrangement for recording a variable width analogue audio sound track.
The audio modulation, i.e. the sound, can be recovered by suitably gathering, for example by means of a photo detector, illumination transmitted through the sound track area. The signal from the photo detector can then be used as input to the audio system/loudspeakers.
This technique can be subject to imperfections, physical damage and contamination during recording, printing and subsequent handling. Since these recording techniques use photographic film, the exposure time is a critical parameter. In addition can imperfections occur, for example the density of the exposed or unexposed areas can vary randomly or in sections across or along the sound track area. During audio track playback such density variations can directly translate into spurious noise components interspersed with the wanted audio signal.
Further the sound track must be copied to the image film in a succeeding process, which causes further possibilities for errors.